affixation vs combining

affixation and combining both are nouns.

Word	Noun	Adjective	Verb	Adverb
affixation	Yes	No	No	No
combining	Yes	No	No	No

As nouns, combining is a hypernym of affixation; that is, combining is a word with a broader meaning than affixation:

Other hypernyms of affixation include combination, compounding.

affixation (noun)	combining (noun)
formation of a word by means of an affix	the act of combining things to form a new whole
the act of attaching or affixing something	an occurrence that results in things being united
the result of adding an affix to a root word